Essential Revision Notes for MRCP Third Edition - PasTest

Essential Revision Notes for MRCPTable 1.6. Guide to the timing of changes in cardiac enzymesMarkerInitialrisePeakReturn tonormalNotesCreatine phosphokinase* 4–8 h 18 h 2–3 days CPK-MB is main cardiac isoenzymeMyoglobin 1–4 h 6–7 h 24 h Low specificity from skeletal muscle damageTroponin** 3–12 h 24 h 3–10 days Troponins I and T are the most sensitive andspecific markers of myocardial damageavailableLactate dehydrogenase(LDH)10 h 24–48 h 14 days Cardiac muscle mainly contains LDH* Creatine phosphokinase has three isoenzymes, of which the CPK-MB isoenzyme is most cardiac-specific,although numerous other organs possess the enzyme in small quantities. A CPK-MB of .2.5% of the total CPK hasbeen suggested as very specific for MI in the context of chest pain. This is inaccurate in situations of significantacute or chronic skeletal injury, where CPK levels will be high** Troponin interpretation is specific to the assay used and local guidelines should be consulted. A level greaterthan the 99th centile for the assay is regarded as positive. Assays may be read only, semi-quantitative orquantitative. Positives occur in all conditions where myocardial damage occurs, including pulmonary embolus,myocarditis, extreme bradycardia or tachycardia, sepsis, renal impairment and uncontrolled diabetes mellitus• Complications of inferior infarctions• Higher re-infarction rate• Inferior aneurysm – with mitralregurgitation (rare)• Pulmonary embolism (rare)• Complete heart block and other degreesof heart block• Papillary muscle dysfunction and mitralregurgitation• Right ventricular infarcts need highfilling pressures (particularly if posteriorextension)*Although warfarin provides no general benefit, it mayreduce the overall CVA rate (1.5%–3.6%) in thosepatients with echocardiographically demonstrable muralleft ventricular thrombus after a large anterior MI, sorecommended for up to 6 months after the infarctionHeart block and pacing after myocardialinfarction• Temporary pacing is indicated in anterior MIcomplicated by complete heart block. Thispresentation is associated with high mortalitydue to the extensive myocardial damage. Thedecision as whether to temporarily pace apatient with inferior infarction and completeheart block is primarily dictated by the patient’shaemodynamic status. Atropine andisoprenaline can also be tried. Narrow-complexescape rhythms are more stable. Anobservational period of 7 days post-MI isappropriate to allow the return of sinus rhythmbefore considering permanent pacing• The right coronary artery is the dominant vessel(over left circumflex) in 85% of patients. As thisgives off branches to SA and AV nodes, heart34